1. Field of the Invention
The present invention relates generally to a coordinate input device and in particular, to coordinate input device for manual character input and two- or three-dimensional coordinate input for a computer.
2. Description of the Related Art
As shown in FIG. 2, a conventional coordinate input device is formed of an acceleration detector 1, a first integrator 3, and a second integrator 5. In order to obtain the spatial coordinates at the tip of a coordinate indicator, the acceleration detector 1 detects two-dimensional accelerations of the tip of the coordinate indicator using an acceleration detector fixed at the tip of a pen-type coordinate indicator to detect two-directional accelerations in perpendicular planes. The first integrator 3 integrates the acceleration of the tip of the coordinate indicator output by the acceleration detector 1 to obtain the velocity at the tip thereof. The second integrator 5 integrates the velocity of the tip of the coordinate indicator output by the first integrator 3 to obtain the spatial coordinates at the tip of the coordinate indicator. Such a coordinate input device is disclosed, for example, in Japanese patent Application Laid-open No. 156519-1991.
However, there has been a disadvantage in that the above conventional coordinate input device can input only two-dimensional coordinates and cannot input three dimensional coordinates. Furthermore, when a pen acting as a coordinate indicator is tilted or changed in its attitude or rotational orientation, the effect of gravity causes an erroneous determination of the acceleration of the pen, thus making it difficult to perform accurate coordinate input. Further, when a pen is tilted but the position of the tip is not changed, the device erroneously detects such movement as a change in the position of the tip, resulting in further inaccuracy of conventional coordinate input devices.
Furthermore, there has been a disadvantage in that the conventional coordinate input device, as shown in FIG. 21, requires periodical initializing because the error in the position which is obtained by twice integrating detected acceleration values diverges significantly even when a small noise signal is erroneously detected as acceleration of a pen.